JS判断一个字符串是不是含有重复字符

function fun(){
			var str = "DCF";
			var arrays = new Array();
			var flag = true;
			for(var i=0;i<str.length;i++){
				var temS = str.charAt(i);
				if(str.replace(temS,"").indexOf(temS) > -1){
					flag = false;
					break;
				}
				arrays.push(temS);
			}
			if(flag){
				str = arrays.sort().join("");
			}else{
				str = "";
			}
			alert(str);
		}